Hematopoietic stem cell transplantation is a form of stem cell therapy used to treat cancers such as lymphoma and leukemia and other blood-related diseases. However, there currently are several drawbacks in the use of bone marrow hematopoietic cell transplantation. Most importantly, the donor pool is limited by the need for at least partial HLA matching, and this delays the finding of a suitable donor. Human umbilical cord blood (hUCB) is increasingly being used as an alternative source of HSC/HPC cells for allogeneic HSCT. However, the absolute number of hUCB HSCs transplanted is much lower than bone marrow cells, and results in significantly delayed engraftment. The proposed studies are to test the efficacy and safety of TAT-SALL4 in reducing the number of hUCB HSCs required for short and long-term engraftments following irradiation, through expansion of HSCs/HPCs in vivo. One of main goals in this proposal is to develop a safe strategy of using a TAT-SALL4 protein for hematopoietic stem cell therapies. Most importantly, our work would greatly impact the field with improved patient outcomes, broader patient usage and possibly lead to the use of just a single umbilical cord for transplantation of HSCs in adults suffering fro acute radiation syndrome, lymphoma, leukemia, or other blood-related diseases.